dnsop J. Appelbaum
Internet-Draft The Tor Project, Inc
Intended status: Standards Track A. Muffett
Expires: December 21, 2015 Facebook
June 19, 2015
The .onion Special-Use Domain Name
draft-ietf-dnsop-onion-tld-00
Abstract
This document registers the ".onion" Special-Use Domain Name.
Status of This Memo
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Appelbaum & Muffett Expires December 21, 2015 [Page 1]Internet-Draft .onion June 2015Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. The ".onion" Special-Use Domain Name . . . . . . . . . . . . 2
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Tor network [Dingledine2004] has the ability to host network
services using the ".onion" Special-Use Top-Level Domain. Such
addresses can be used as other domain names would be (e.g., in URLs
[RFC3986]), but instead of using the DNS infrastructure, .onion names
functionally correspond to the identity of a given service, thereby
combining location and authentication.
In this way, .onion names are "special" in the sense defined by
[RFC6761] Section 3; they require hardware and software
implementations to change their handling, in order to achieve the
desired properties of the name (see Section 4). These differences
are listed in Section 2.
Like Top-Level Domain Names, .onion addresses can have an arbitrary
number of subdomain components. This information is not meaningful
to the Tor protocol, but can be used in application protocols like
HTTP [RFC7230].
See [tor-address] and [tor-rendezvous] for the details of the
creation and use of .onion names.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. The ".onion" Special-Use Domain Name
These properties have the following effects upon parties using or
processing .onion names (as per [RFC6761]):
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1. Users: human users are expected to recognize .onion names as
having different security properties, and also being only
available through software that is aware of onion addresses.
2. Application Software: Applications (including proxies) that
implement the Tor protocol MUST recognize .onion names as special
by either accessing them directly, or using a proxy (e.g., SOCKS
[RFC1928]) to do so. Applications that do not implement the Tor
protocol SHOULD generate an error upon the use of .onion, and
SHOULD NOT perform a DNS lookup.
3. Name Resolution APIs and Libraries: Resolvers MUST either either
respond to requests for .onion names by resolving them according
to [tor-rendezvous] or by responding with NXDOMAIN.
4. Caching DNS Servers: Caching servers SHOULD NOT attempt to look
up records for .onion names. They MUST generate NXDOMAIN for all
such queries.
5. Authoritative DNS Servers: Authoritative servers MUST respond to
queries for .onion with NXDOMAIN.
6. DNS Server Operators: Operators MUST NOT configure an
authoritative DNS server to answer queries for .onion. If they
do so, client software is likely to ignore any results (see
above).
7. DNS Registries/Registrars: Registrars MUST NOT register .onion
names; all such requests MUST be denied.
3. IANA Considerations
This document registers "onion" in the registry of Special-Use Domain
Names [RFC6761]. See Section 2 for the registration template.
4. Security Considerations
.onion names are often used to provide access to end to end
encrypted, secure, anonymized services; that is, the identity and
location of the server is obscured from the client. The location of
the client is obscured from the server. The identity of the client
may or may not be disclosed through an optional cryptographic
authentication process.
These properties can be compromised if, for example:
o The server "leaks" its identity in another way (e.g., in an
application-level message), or
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o The access protocol is implemented or deployed incorrectly, or
o The access protocol itself is found to have a flaw.
.onion names are self-authenticating, in that they are derived from
the cryptographic keys used by the server in a client verifiable
manner during connection establishment. As a result, the
cryptographic label component of a .onion name is not intended to be
human-meaningful.
The Tor network is designed to not be subject to any central
controlling authorities with regards to routing and service
publication, so .onion names cannot be registered, assigned,
transferred or revoked. "Ownership" of a .onion name is derived
solely from control of a public/private key pair which corresponds to
the algorithmic derivation of the name.
Users must take special precautions to ensure that the .onion name
they are communicating with is correct, as attackers may be able to
find keys which produce service names that are visually or
semantically similar to the desired service.
Also, users need to understand the difference between a .onion name
used and accessed directly via Tor-capable software, versus .onion
subdomains of other top-level domain names and providers (e.g., the
difference between example.onion and example.onion.tld).
The cryptographic label for a .onion name is constructed by applying
a function to the public key of the server, the output of which is
rendered as a string and concatenated with the string ".onion".
Dependent upon the specifics of the function used, an attacker may be
able to find a key that produces a collision with the same .onion
name with substantially less work than a cryptographic attack on the
full strength key. If this is possible the attacker may be able to
impersonate the service on the network.
If client software attempts to resolve a .onion name, it can leak the
identity of the service that the user is attempting to access to DNS
resolvers, authoritative DNS servers, and observers on the
intervening network. This can be mitigated by following the
recommendations in Section 2.
5. ReferencesAppelbaum & Muffett Expires December 21, 2015 [Page 4]Internet-Draft .onion June 20155.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, February 2013.
5.2. Informative References
[Dingledine2004]
Dingledine, R., Mathewson, N., and P. Syverson, "Tor: the
second-generation onion router", 2004, <https://www.onion-
router.net/Publications/tor-design.pdf>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928, March
1996.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
[tor-address]
Mathewson, N. and R. Dingledine, "Special Hostnames in
Tor", September 2001,
<https://gitweb.torproject.org/torspec.git/plain/address-
spec.txt>.
[tor-rendezvous]
Mathewson, N. and R. Dingledine, "Tor Rendezvous
Specification", April 2014,
<https://gitweb.torproject.org/torspec.git/plain/rend-
spec.txt>.
Appendix A. Acknowledgements
Thanks to Roger Dingledine, Linus Nordberg, and Seth David Schoen for
their input and review.
This specification builds upon previous work by Christian Grothoff,
Matthias Wachs, Hellekin O. Wolf, Jacob Appelbaum, and Leif Ryge to
register .onion in conjunction with other, similar Special-Use Top-
Level Domain Names.
Appelbaum & Muffett Expires December 21, 2015 [Page 5]Internet-Draft .onion June 2015Authors' Addresses
Jacob Appelbaum
The Tor Project, Inc
Email: jacob@appelbaum.net
Alec Muffett
Facebook
Email: alecm@fb.com
Appelbaum & Muffett Expires December 21, 2015 [Page 6]